This study was initiated to determine the structure: function relationships of the components of RNA polymerase II transcription complex in Drosophila melanogaster. RNA polymerase II is a heteromultimer consisting of approximately ten different subunits, each of which is presumably specified by a different locus. The number of associated transcription factors (which are not structurally a part of RNA polymerase II) is unknown, but evidence for their existence has been found in other systems. To date only the genetic locus which specifies Alpha-amanitin-resistance to RNA polymerase II has been identified. That locus has been cloned out and its DNA is being analyzed to determine which subunit it encodes and the nature of the genetic control at the locus.